I've wanted a mobile second display for a while. I'd prefer something that had more than just USB-C, though.
I don't use my laptop much while actually moving around, but instead I bring it places and set it up with a mouse and sometimes even keyboard. This would make it an even more versatile mobile workstation that you can deploy.
Thanks for those who've recommended Duet for the iPad. I've looked into that and it looks great -- though sadly won't work on my 1st gen iPad (was hoping to find a good use for it).